In producing a non-aqueous secondary battery such as a lithium-ion secondary battery, etc., for instance, a positive electrode, a negative electrode and a non-aqueous electrolyte solution are assembled and the assembly is then subjected to an activation process. For instance, Patent Document 1 discloses a method for producing a lithium-ion secondary battery comprising lithium bis(oxalato)borate (LiBOB, Li[B(C2O4)2]) in a non-aqueous electrolyte solution. The production method comprises an aging step where, after an initial charge, a sealed battery case is stored in a high-temperature environment; a degassing step where the aged battery case is unsealed; and a final sealing step where the degassed battery case is sealed again.